Radar sensors can be used in motor vehicles preferably for measuring distances and relative velocities of vehicles traveling one behind the other. Such a proximity radar system is usually referred to in the literature as an Autonomous/Intelligent Cruise Control (AICC/ICC) or Adaptive Cruise Control (ACC). The system generates either a collision warning signal or automatically controls the brakes or the drive of the motor vehicle if the distance to a vehicle traveling ahead drops below a minimum permissible value.
European Patent No. 0 568 427 describes a radar sensor, in which a plurality of transmitting antenna elements and a plurality of receiving antenna elements are arranged separately from one another. The transmitting antenna elements generate a multibeam radiation pattern, and an array of receiving antenna elements installed in front of the transmitting antenna elements receives the radar beams (radar echos) reflected from one or more objects. The receiving elements are arranged in the transmission range of, and oriented in the same direction as, the transmitting antenna elements. If both the radar transmitter and the radar receiver are to be supplied from the same oscillator to minimize costs, relatively long high-frequency lines are needed in the case of the known antenna arrangement, since the outputs of the receiving antenna elements must be run via long, circuitous routes to a common oscillator arranged near the inputs of the transmitting antenna elements. Long lines, on the other hand, have the disadvantage that they generate relatively high losses.
An object of the present invention is to provide a radar sensor which requires the shortest possible lines in order both to supply the transmitting antenna element with the carrier signal of an oscillator and to demodulate the output signals of the receiving antenna element with the same oscillator carrier signal.